This invention relates to a synchronization detector for detecting synchronization signals from frames that are included in a sector with a predetermined format.
Now, it is studied to digitize a video signal to store the digitized video signal into a memory medium, and to play back the digitized video signal memorized in the memory medium. Generally, the video signal is much larger than an audio signal in information amount. Accordingly, it is necessary that the memory medium has a very large capacity and can operate at high speed. In addition, it is necessary and indispensable to compress the video signal.
Since a digital versatile (or video) disk (DVD) is superior to a CD-ROM in quality of picture and playback time, it attracts considerable attention as the memory medium and is being realized. Moreover, JPEG (Joint Photographic Experts Group) and MPEG (Moving Picture Experts Group) 1 and 2 are known as the technique for compressing the video signal and for storing the video signal into the memory medium, such as the DVD. The JPEG is used for dealing with a still picture while the MPEG 1 and 2 are used for dealing with a moving picture.
Under these circumstances, a data format for the DVD is different from a data format for the CD-ROM. The data format for the DVD includes a sector comprising a predetermined digital signal unit. The sector is divided into a plurality of frames, for example, twenty-six frames. Each of the frames includes a synchronization signal together with a modulated digital video signal and error correction codes. The synchronization signal has thirty-two channel bits and has an individual pattern and a common pattern. The individual pattern is independent of other individual patterns included in other frames of the sector. For example, eight individual patterns are prepared for the sector. The common pattern is the same as in the other frames of the sector.
In a case that the digital video signal having the data format are played back, the synchronization signal located in the sector must be correctly reproduced to play back the digital video signal. Namely, a synchronization detector is very important for playing back the digital video signal.
If the synchronization detector make an error in detection for a head frame of the sector, the digital video signal will be incorrectly played back. Namely, when the synchronization signal of the head frame is incorrectly detected, an ID information can not be obtained. The ID information is added to a head of a sector, which comprises a plurality of the sectors and is a unit of error correction. Thus, it becomes difficult to play back the digital video signal in this case.
Moreover, if the synchronization detector make an error in detection for a middle frame of the sector, a reproduction track of the DVD deviates from correct track. Accordingly, the digital video signal is incorrectly played back in this case, too.
It is therefore an object of this invention to provide a synchronization detector which is capable of detecting a location of a frame when a synchronization signal included in the frame is not detected.
It is another object of this invention to provide a synchronization detector which is capable of detecting a head of a sector when a synchronization signal included in a head frame of the sector is not detected.
It is still another object of this invention to provide a synchronization detector which is capable of detecting a gap between an aimed reproduction track and a practical reproduction track.
Other object of this invention will become clear as the description proceeds.
On describing the gist of this invention, it is possible to understand that a synchronization detector detects synchronization signals from frames which are included in a sector with a predetermined format. The synchronization signals are located in the frames, respectively, with a predetermined order.
According to the gist of this invention, the synchronization detector comprises an extracting section which extracts the synchronization signals from the sector to produce extracted signals which are representative of the synchronization signals. A location detecting section is connected to the extracting section and detects locations of the frames on the basis of the extracted signals to produce frame location signals which are representative of the locations.
According to another gist of this invention, the extracting section has a register section to store at least three successive extracted signals. The location detecting section has a decoder to produce the frame location signal on the basis of relationship among the extracted signals stored in the register section, a pointer section for counting the number of the frame location signal to produce a frame number signal, and a comparing circuit for comparing the frame location signal with the frame number signal.